1. Field of the Invention
The present invention relates generally to a method for producing hydrocarbons from a reservoir traversed by a lateral or horizontal wellbore. More particularly, the subject invention concerns a wellbore having an inverted or upwardly inclining producing interval and a method for drilling, completing, and producing from such a wellbore.
2. Description of the Related Art
A conventional method to produce hydrocarbons has been to drill a wellbore in an essentially vertical direction through the subterranean reservoir. In reservoirs that are relatively thin, this method exposed only a small portion of the pay zone, or producing formation, to the wellbore. Premature gas coning and/or water coning in such wells often reduced the amount of oil that could be recovered.
Within the past decade it has become increasingly common to drill at least a portion of the wellbore so that it intersects the reservoir at an angle to the vertical. In some cases this is a high angle of from 83 to about 88 degrees, or even horizontal. High angle or horizontal sections can then be extended laterally through the pay zone 1000 to 3000 feet or more, or through a plurality of pay zones which may be separated by fault blocks, shale stringers, or other barriers to horizontal or vertical permeability. Development of high angle drilling techniques has meant that more of the pay zone can be exposed to the wellbore, and that oil can be produced at a faster rate while potentially recovering more of the original oil in place than would be otherwise possible with a conventional directional well (less than 83 degrees).
Despite the advantages of high angle wells, they present unique problems and challenges. A driller is allowed a very small margin of error in placing the wellbore within the vertical target range, particularly if the pay zone is thin, faulted, or dipping. For reservoirs having two or more fluids, it is also desirable to locate the completed zones of the wellbore some distance away from the gas-oil or oil-water interfaces to minimize the chances of premature gas or water coning.
Coning in a high angle oil well can be a serious problem. Gas cone breakthrough normally occurs at the highest (shallowest) point in the wellbore that is open to production, and water cone breakthrough normally occurs at the lowest (deepest) point open to production. The gas or water dilutes the oil to the extent that continued production from the well becomes uneconomic.
Downwardly inclining completion intervals lend themselves more readily to the mechanical regulation of water coning. Mechanical regulation of gas coning is more difficult to accomplish by current industry methods. Gas coning in a high angle or horizontal well can be difficult or impossible to repair if the gas entry point occurs at or near the beginning of the producing interval. It is therefore desirable to keep the potential for coning, especially gas coning, to a minimum.